Method of using cytokine receptors on microorganism

ABSTRACT

Cytokine receptors for tumor necrosis factor e which are found on microorganisms may, if bound with exogenous TNFα, enhance the response of natural killer cells activated by the microorganisms, or increase TNFα production by peripheral blood lymphocytes treated with the microorganisms. Microorganisms with receptor-bound exogenous TNFα have enhanced cellular invasion ability which may change the immune response thereto. Clinical and pharmaceutical applications of these discoveries are provided.

The United States government has certain rights in this invention because related research was supported in part by funds from National Institutes of Health Grant No. AI23731.

This is a division of application Ser. No. 07/824,112, filed Jan. 23, 1992, now U.S. Pat. No. 5,270,038, issued Dec. 14, 1993.

BACKGROUND OF THE INVENTION

The invention relates generally to the discovery of cytokine receptors on microorganisms, and more specifically to new methods and products in medical treatment and research related to the discovery. Cytokines produced by monocytes/macrophages are called monokines, and those produced by lymphocytes are called lymphokines. Stimuli for their production include endotoxin and Gram-negative bacteria. One cytokine of particular interest is tumor necrosis factor α (TNFα).

TNFα is an inflammatory cytokine which has numerous biological activities and is believed to play important roles, not only in host defense but also in some of the pathological sequelae associated with bacterial infections. Receptor(s) for TNFα are found on most somatic cells, and they have recently been characterized and cloned. Biological effects of TNFα and other cytokines binding to eukaryotic cells are well known.

For example, it is now well established that cytokines play important roles in regulating aspects of the immune response. Cytokines have been shown to be essential for host defense against viruses, tumors and bacterial infections. There is, however, a delicate balance between when a cytokine is advantageous to a host and when it contributes to the pathology of a disease. Thus, knowledge of how to make the choice between administering a cytokine and blocking its action in a disease process could be a valuable tool in clinical medicine. The need for such knowledge is rapidly increasing as cytokines and cytokine blockers become more readily available.

Many cytokines have now been cloned and new cytokines are constantly being discovered and cloned. Recombinant cytokines are now also being used in clinical trials all over the world. Recently, much attention has been focused on identifying and cloning cytokine receptors on eukaryotic cells previously identified as being targets for the many cytokines produced by the immune system. But similar work on pathogenic cells such as bacteria has not been published; there are no reports of TNFα or any other cytokine binding to bacteria until quite recently (1A).

SUMMARY OF THE INVENTION

The present invention concerns findings that microorganisms, including bacteria and imperfect fungi, have cytokine receptors. A microorganism receptor for TNFα is of particular interest. With receptor-bound TNFα microorganisms more effectively enhance natural killer (NK) cell activity and induce the production of TNFα by human peripheral blood lymphocytes (PBL's). Further, bacteria with receptor-bound TNFα are taken up by macrophages and epithelial cells to a much greater extent than bacteria without receptor-bound TNFα. Although it is known that many cytokines are produced as a consequence of bacterial interaction with monocytes/macrophages or lymphocytes, there are few reports of bacteria and none of imperfect fungi having receptors for cytokines. None previously have reported microorganisms becoming more immunogenic as a result of bound cytokine effects. In this regard, it was found that coating S. typhimurium with TNFα resulted in a complex which induced higher levels of antibody in vivo to this bacterium as compared to animals given uncoated bacteria.

One form of the invention is a composition comprising microorganisms having receptors for TNFα or other cytokines, with exogenous cytokines such as TNFα bound thereto. These are novel compositions of matter which those skilled in the art will recognize as having many uses. Specific applications include those where the source of exogenous cytokines such as TNFα is living eukaryotic cells, as well as those where the source is a recombinant microorganism or process based thereon.

Among the microorganisms to which the invention may be applied are Gram-positive or Gram-negative bacteria, as well as imperfect fungi. Specific examples of microorganisms to which the invention may be applied include Candida albicans, Salmonella typhimurium, Shigella flexneri, and Escherichia coli. Those skilled in the art will recognize that any microorganism with receptors for cytokines, including TNFα, can be used in applications of the invention.

The compositions or methods of the invention may be used for activating human NK cells by treating them with microorganisms having receptors for TNFα or other cytokines to which exogenous TNFα or other cytokines have been bound. Analogously, human PBL's may be treated with microorganisms having receptor-bound exogenous TNFα or other cytokines to stimulate the production of additional cytokines such as TNFα by the PBL's. Other cells may be substituted for the human NK and PBL cells in these applications.

The cellular invasion ability of microorganisms may be enhanced by application of the invention by binding exogenous TNFα or other cytokines to microorganism receptors. Because alteration of the cellular invasion ability of a microorganism changes the cellular response to such microorganisms, the immune response will also change. Those skilled in the art will appreciate that vaccines comprised of components with enhanced invasion ability may have improved efficacy.

Applications of the invention include the use of bacterial-derived receptors for TNFα or other cytokines for isolating an purifying particular cytokines. Additionally, a more effective clinical treatment of diseases involving the modulation of the immune system by inhibiting or enhancing the effects of TNFα or other cytokines is feasible. Pharmaceutical applications of the invention may include the use of bacteria with receptor-bound TNFα or another cytokine to make the bacteria better antigens and thereby improve the efficacy of vaccines by enhancing host immune response. The latter application may include preparation of vaccines for human and animal use. Those skilled in the art will recognize that other cytokines may substitute for TNFα, depending on the application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Saturation binding curve of ¹²⁵ I-TNFα after 40 min at 37° C. with Shigella flexneri.

FIG. 2. Time course of ¹²⁵ I-TNFα binding by Shigella flexneri at 37° C. showing binding is saturable, with optimal binding occurring at 40 minutes at 37° C.

FIG. 3. Competition of TNFα (open circles) and TNFβ (solid circles) with ¹²⁵ I-TNFα for binding to Shigella flexneri. Unlabeled TNFβ is ineffective at competing with ¹²⁵ I-TNFα. FIG. 3A shows Scatchard analysis indicating a Kd of 2.5 nM, with 276 binding sites for TNFα per bacterium.

FIG. 4. HeLa cell invasion by (virulent) S. flexneri (SA100) is increased up to 20-fold in bacteria pretreated with TNFα, compared with invasion by untreated bacteria.

FIG. 5. HeLa cell invasion by (avirulent) S. flexneri (SA100NI) is essentially unchanged in bacteria pretreated with TNFα, compared with invasion by untreated bacteria.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relies in part on the fact that receptors for cytokines such as TNFα are found on microorganisms such as Gram-negative bacteria, Gram-positive bacteria, and the yeast form of Candida albicans. Other aspects of the invention derive from the fact that bacteria with receptor-bound TNFα enhance NK cell activity (Table 1) and induce TNFα production from human PBL's (Table 2) to a much greater extent than bacteria without receptor-bound TNFα. Such bacteria are also taken up by macrophages and epithelial cells more avidly than bacteria without TNFα on their surface, viz., a virulence property is altered by the presence of TNFα. Coating bacteria with TNFα resulted in a more immunogenic antigen which resulted in higher levels of antibody being produced in mice (Table 4). These observed TNFα-related effects support the claimed clinical and laboratory applications in the present invention. Those skilled in the art will recognize that both other cytokines and other microorganisms than those exemplified herein may be quite analogously utilized.

                  TABLE 1                                                          ______________________________________                                         NK cell activation by TNFα coated bacteria                                             NK cell activity                                                                ##STR1##                                                        Culture conditions                                                                             3:1        12:1   50:1                                         ______________________________________                                         Human PBL plus:                                                                Medium           3         10     32                                           IL2             15         40     60                                           S. flexneri      6         14     38                                           S. flexneri coated                                                                             10         25     49                                           with TNFα                                                                S. typhimurium   8         12     30                                           S. typhimurium coated                                                                          13         29     52                                           with TNFα                                                                ______________________________________                                          Human PBL are incubated 18 hr with one of the following: 1) IL2 500 u/ml,      2) 10.sup.5 CFU of S. flexneri either untreated or coated with TNFα      or 3) 10.sup.5 CFU of S. typhimurium either untreated or coated with           TNFα. NK cell activity is assessed using a 4 hr .sup.51 Cr release       assay with K562 tumor cells.                                             

                  TABLE 2                                                          ______________________________________                                         TNF production by human PBL stimulated with                                    TNFα-coated S. flexneri                                                  Culture conditions                                                                               TNF u/ml                                                     ______________________________________                                         Human PBL plus:                                                                Medium            12                                                           S. flexneri       13                                                           S. flexneri coated with                                                                          109                                                          TNFα                                                                     ______________________________________                                          Human PBL are incubated 18 hr with 1) medium, 2) S. flexneri, or 3) S.         flexneri coated with TNFα. Supernatants from these cultures are          assessed for TNF bioactivity using the L929 assay.                       

The following examples are presented to describe preferred embodiments and utilities of the present invention and are not meant to limit the present invention unless otherwise specified in the claims appended hereto. Taken together, the examples illustrate the best mode of implementing the invention as it is currently understood.

EXAMPLE 1 TNFα binding to Shigella flexneri

TNFα binding to a Shigella flexneri is investigated using ¹²⁵ I-labeled human recombinant TNFα and bacterium-¹²⁵ I-TNFα complexes quantitated by filtration. ¹²⁵ I-labeled recombinant human TNFα (200-800 Ci/mMol) is obtainable from Amersham Corp., Arlington Heights, Ill., or may be produced using the iodogen method with rhTNFα obtained from UBI Inc., Lake Placid, N.Y. Unlabeled recombinant human TNFα (2×10⁷ units/mg) and TNFα (3×10⁷ units/mg) are available from Genzyme, Boston, Mass. Bacteria from overnight cultures of S. flexneri serotype 2a, strain SA100 are grown to mid-logarithmic phase, then incubated 10 min at 37° C. with 0.01% azide in RPMI medium. Four Shigella flexneri strains of this serotype are available from the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852-1776. Treated-bacteria (2×10⁹ cfu) are then washed and incubated in 250 μl of PBS containing 1% heat inactivated FCS or 1% BSA plus varying concentrations of labeled or unlabeled TNFα or TNFβ. After appropriate incubation at 37° C. with mixing every 10 min, bacteria-TNF mixtures are transferred to a syringe (10 ml) equipped with a 0.45 μm nitrocellulose filter. Tubes (BSA-coated microfuge) which contained bacteria-TNF mixtures are washed with 250 μl of RPMI, and this volume added to the syringe-filter. Bacteria are then isolated by filtration and filters containing bacteria washed with 1 ml of RPMI. Filters are then assessed for the amount of bound ¹²⁵ I-TNFα. Filters used in these experiments are pretreated with FCS. ¹²⁵ I-TNFα binding to filters in the absence of bacteria is ≦6% of the total cpm added to the binding mixture. This value is always subtracted from cpm obtained from ¹²⁵ I-TNF-bacteria complexes isolated by filtration. Non-specific binding to bacteria is assessed using ≧100-fold excess of unlabeled TNFα. Non-specific binding is usually about 10% of total bound cpm. Scatchard analysis is performed as described by Stuart.

¹²⁵ I-TNFα binding to S flexneri varies among different commercial lots of ¹²⁵ I-TNFα. This appears to correlate with the level of biological activity retained by the ¹²⁵ I-labeled TNFα. Little binding is detected when ¹²⁵ I-TNFα has <20% of its biological activity as measured by the L-929 bioassay. In this regard, over one-half of the commercially obtained lots of ¹²⁵ I-TNFα have lost 80-90% of their biological activity and give low levels of binding to S. flexneri.

¹²⁵ I-TNFα binding to azide-treated versus untreated bacteria is identical during the first 20 min of incubation. However, untreated bacteria have a doubling time of around 30-40 min and consistently bind more TNFα than azide-treated bacteria at time periods longer than 20 min. Data presented above and in Table 1 are obtained using azide-treated bacteria when binding is assessed at 37° C. Non-azide-treated bacteria are used when binding is assessed at 4° C., which is optimal at 4 hr incubation. Scatchard analysis of data obtained from binding experiments done at 4° C. gives a Kd of 3.0 nM with 215 binding sites for TNFα per bacterium.

As illustrated in FIGS. 1-3, S. flexneri binds significant levels of ¹²⁵ I-TNFα. This binding is saturable with optimal binding occurring at 40 min when binding is performed at 37° C. (FIGS. 1 & 2). FIG. 2 shows the time course of ¹²⁵ I-TNFα binding using 0.1 nM ¹²⁵ I-TNFα (3-4×10⁴ cpm). When binding is measured at 4° C., optimal binding occurs at 4 hr. FIG. 3 shows the competition of TNFα and TNFβ with ¹²⁵ I-TNFα for binding to S. flexneri. FIG. 3A shows Scatchard analysis indicating a Kd of 2.5 nM, with 276 binding sites for TNFα per bacterium. The binding of ¹²⁵ I-TNFα to S. flexneri is inhibited by various concentrations of unlabeled TNFα, but unlabeled TNFβ is ineffective at competing with ¹²⁵ I-TNFα. In contrast, TNFα receptors on eukaryotic cells can be occupied by both TNFα and TNFβ. Thus, the bacterial receptors for TNFα appear to differ from TNFα receptors on eukaryotic cells with regard to binding specificity for TNFα versus TNFβ.

EXAMPLE 2 TNFα binding to bacteria

The ability to bind TNFα is not exclusive to Shigella flexneri. An avirulent Escherichia coli and a virulent Salmonella typhimurium both bind significant levels of ¹²⁵ I-TNFα (Table 3). Further, both a virulent (SA100) and an isogeneic non-pathogenic S. flexneri strain (SA100NI) appear to bind comparable levels of ¹²⁵ I-TNFα (Table 3). These data indicate that bacteria-TNFα binding may be common property of both virulent and avirulent gram-negative bacteria.

No difference is found between the levels of TNFα bound by rough versus smooth strains of Salmonella. However, heating, (52° C./3 min), formalin fixation or trypsin treatment of bacteria results in complete to partial reduction of TNFα binding (Table 3), indicating that bacteria-encoded protein forms at least a part of the TNFα receptor.

                  TABLE 3                                                          ______________________________________                                         TNFα binding to bacteria                                                                 TNFα                                                                     Specific binding (cpm) at:                                     Bacterium         4° C.                                                                               37° C.                                    ______________________________________                                         Exp. 1 S. flexneri (SA100NI)                                                                          6591 ± 124                                                                             5994 ± 404                                       E. coli        5801 ± 58                                                                               6150 ± 150                                       S. typhimurium  4951 ± 160                                                                             5850 ± 300                                Exp. 2 S. flexneri (SA100)                                                            untreated      7065 ± 48                                                                               5226 ± 73                                        formalin-fixed 5818 ± 33                                                                               4176 ± 66                                        heat-treated   3199 ± 91                                                                               3056 ± 8                                  Exp. 3 S. flexneri (SA100)                                                            untreated      3588 ± 99                                                    trypsin-treated                                                                                327 ± 97                                             Exp. 4 C. albicans     6053 ± 120                                                                             5410 ± 91                                 ______________________________________                                          .sup.125 I-TNFα binding to different bacteria was assessed. Bacteri      (2 × 10.sup.9) are incubated with 0.1 nM .sup.125 ITNFα (3- 4      × 10.sup.4 cpm) for 40 min at 37° C. or for 4 hr at 4.degree      C. A laboratory strain of E. coli (DH5α) and a rough strain of S.        typhimurium (TML) are grown and treated as described in FIG. 1 for S.          flexneri. Candida albicans were grown to midlogarithmic phase and washed       twice.  .sup.125 IINFα binding to Candida albicans was assessed          using 5 × 10.sup.7 organisms and using assay conditions exactly as       described for .sup.125 ITNFα binding to bacteria. S. flexneri are        also assessed for TNFα binding following heat treatment (52°      C. for 3 min), fixation by 1% formaldehyde, or by trypsin treatment.           Trypsin treatment of bacteria is achieved by incubating 4 × 10.sup.      S. flexneri (SA100) in  10 ml of PBS with trypsin (100 μg/ml, Sigma,        St. Louis, MO) for 30 min at 37° C. Soybean trypsin inhibitor (100      μg/ml, Sigma) is then added and after 15 min at 37° C. the           bacteria are pelleted and washed. Trypsin treated or control treated           bacteria are then assessed for their ability to bind .sup.125 ITNFα      as described in FIG. 1. Data presented are the mean (SD) of duplicated         determinations.                                                          

EXAMPLE 3 Biological consequences of TNFα binding to Shigella flexneri

Important virulence factors of S. flexneri are its ability to penetrate and replicate within epithelial cells of the intestinal mucosa, resulting in subsequent tissue damage. These factors are investigated in HeLa cells by pretreatment of S. flexneri SA100 with TNFα. S. flexneri (SA100 or SA100NI) are incubated in 1 ml of RPMI-1640 with or without varying concentrations of TNFα. After 4 hr at 4° C., bacteria (10³ cfu/ml) are pelleted by centrifugation (1500 xg) and washed once with 4 ml of RPMI. Bacteria (pretreated with media vs TNFα) are then assessed for their ability to invade HeLa cells. HeLa cell invasion is assessed by using an agarose-agar overlaying procedure as previously described.

Data presented are from triplicate determinations and from one representative experiment of 10 experiments. The results show a dramatic enhancement of HeLa cell invasion (FIG. 4). S. flexneri SA100 (10³ cfu) pretreated with 5000 U of TNFα for 4 hr at 4° C. and then washed twice has a 20-fold enhancement in cellular invasion.

It is apparent that enhancement of cellular invasion is dependent upon bacterial virulence factor(s) because non-invasive S. flexneri can not be converted to an invasive form by ¹²⁵ I-TNFα binding. A non-invasive isogeneic variant of S. flexneri, SA100NI, which binds equivalent levels of ¹²⁵ I-TNFα (Table 3) does not invade HeLa cells after TNFα pretreatment (FIG. 5). The mechanism(s) involved in the enhanced cellular invasion by TNFα-Shigella complexes is unknown, but could possibly result from enhanced interaction with the cell surface.

EXAMPLE 4 Enhanced Immunogenic Potential of ¹²⁵ I-TNFα-coated S. typhimurium

Coating a pathogen with a cytokine was found to result in a more immunogenic antigen. Salmonella typhimurium (10⁸) were incubated with rTNFα (10,000 U) in a volume of 250 ml. After 4 hours at 4° C. the bacteria-TNFα complexes were formalin-fixed, washed twice and injected (ip) into C57B1/6 mice. As a control, Salmonella were treated in an identical fashion in medium with no TNF. Mice were bled at 6 days post challenge. Results of a representative experiment are illustrated in Table 4.

                  TABLE 4                                                          ______________________________________                                         Enhanced Antibody Production in vivo by                                        TNF-Coated S. Typhimurium                                                                      Antibody to TML                                                Mice Immunized With                                                                            ELISA Assay (OD Units)                                         ______________________________________                                         S. typhimurlium (TML)                                                                          .6523 ± .15                                                 S. typhimurlium (TML)                                                                          1.075 ± .31                                                 coated with TNFα                                                         ______________________________________                                          C57B1/6 mice (5) were challenged (ip) with 10.sup.8 formalinfixed TML          which had been pretreated with 10.sup.4 of rTNFα. Serum from             individual mice were obtained at 6 days and assessed for antibody to TML       by ELISA assay. Data is mean ± SD OD units from 5 mice per group.     

Coating Salmonella with TNFα resulted in an enhanced antibody response to Salmonella. These data indicate that coating a pathogen with TNFα can enhance the immune response to that pathogen. These results could be applied for the preparation of vaccines for both human and animal use. Improved vaccines could result from coating any pathogen with cytokines such as interleukin-1 (IL1), interleukin-2 (IL2) or interferon (IFN). The coating could be easily performed as described above or by cross-linking the cytokine onto the pathogen. Additionally, deactivated microorganisms or antigenic microorganism surface components retaining bound cytokines could be used as administered material in the usual course of human or domestic animal vaccination. Oral administration of cytokine-containing avirulent microorganism strains is a preferred mode of immunization, of course when the elicited immunity precludes adverse effects of analogous virulent microorganisms.

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The following references are incorporated in pertinent part in the specification for the reasons therein.

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Changes may be made in the construction, operation and arrangement of the various microorganisms, cytokines, steps and procedures described herein without departing from the concept and scope of the invention as defined in the following claims. 

What is claimed is:
 1. A method for inducing immunity to a Gram-negative bacterial or imperfect fungal microorganism comprising identifying a Gram-negative bacterial or imperfect fungal microorganism having a tumor necrosis factor binding site and administering to an animal a composition including said Gram-negative bacterial or imperfect fungal microorganism or avirulent strain thereof bound to an exogenous tumor necrosis factor at a tumor necrosis factor binding site.
 2. The method of claim 1 wherein said Gram-negative bacterial microorganism is Salmonella typhimurium, Shigella flexneri, or Escherichia coli.
 3. The method of claim 1 wherein said imperfect fungal microorganism is Candida albicans. 